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Proceedings Paper

Analysis of the polarimetric performance of the HARPS3 Cassegrain adaptor unit
Author(s): Patrick Dorval; Frans Snik; Nikolai Piskunov; Ramon Navarro; Jan Kragt; Rik ter Horst; Peter Kunst; Ignas Snellen; Tim Naylor; Samantha Thompson
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Paper Abstract

The third version of the High Accuracy Radial velocity Planet Searcher (HARPS3) instrument is built for a ten-year programme aimed at achieving 10 cm/sec radial velocity precision on nearby stars to search for Earth-like planets. HARPS3 will be commissioned on the to-be-roboticized 2.54-m Isaac Newton Telescope at La Palma in 2021. One of the main changes compared to its predecessors is the novel dual-beam Cassegrain focus, featuring a stabilised beam feed into the HARPS3 spectrograph and an insertable polarimetric sub-unit. This polarimetric sub-unit enables HARPS3 to directly measure stellar activity signatures, which can be useful for correcting activity-induced radial velocity jitter in the search for Earth-like planets. The sub-unit consists of superachromatic polymer quarter- and half-wave retarders for circular and linear polarizations respectively, designed to suppress polarized fringing, and a novel polarimetric beam splitter based on a wire-grid design, separating the two polarimetric beams by 30 mm and feeding two separate science fibers. The dual-beam exchange implementation in combination with the extreme stability of the HARPS3 spectrograph enables a polarimetric sensitivity of 10−5 on bright stars. One of the main challenges of such a system is in the characterization of instrumental polarization effects which limit the polarimetric accuracy of the polarimetric observing mode. By design and characterization of this subsystem and by pre-emptively mitigating possible noise sources, we can minimize the noise characteristics of the polarization sub-unit to allow for precise observations. In this paper we report on the design, realization, assembly, alignment, and testing of the polarimetric unit to be installed in the Cassegrain Adaptor Unit of the HARPS3 spectrograph

Paper Details

Date Published: 20 July 2018
PDF: 8 pages
Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 107026B (20 July 2018); doi: 10.1117/12.2312535
Show Author Affiliations
Patrick Dorval, Leiden Observatory, Leiden Univ. (Netherlands)
Frans Snik, Leiden Observatory, Leiden Univ. (Netherlands)
Nikolai Piskunov, Uppsala Univ. (Sweden)
Ramon Navarro, NOVA Optical IR Instrumentation Group at ASTRON (Netherlands)
Jan Kragt, NOVA Optical IR Instrumentation Group at ASTRON (Netherlands)
Rik ter Horst, NOVA Optical IR Instrumentation Group at ASTRON (Netherlands)
Peter Kunst, NOVA Optical IR Instrumentation Group at ASTRON (Netherlands)
Ignas Snellen, Leiden Observatory, Leiden Univ. (Netherlands)
Tim Naylor, Univ. of Exeter (United Kingdom)
Samantha Thompson, Univ. of Cambridge (United Kingdom)

Published in SPIE Proceedings Vol. 10702:
Ground-based and Airborne Instrumentation for Astronomy VII
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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